The proposed study will investigate if milk immunobiology and volume are associated with enteral health, skin immunity and clinical outcomes in very preterm infants (750 to 1500 gm). Human milk may play a moderating role in the multiple risks these vulnerable infants face, yet the total volume of human milk preterm infants receive is extremely variable. In the Neonatal Intensive Care Unit (NICU) where the study will be performed, only 40% of infants are discharged receiving any human milk at all, and this is not atypical. Little is known about the essential components of preterm mother's milk and whether there may be some components that are critically involved in the most optimal infant outcomes. One hundred maternal-infant dyads will be recruited, with the expectation that at least 75 will continue through the study, and studied for 6-weeks of their stay in the NICU. At each feeding a very small sample will be aliquoted from the milk mothers provide before it is mixed with formula and supplement. These aliquots will be pooled and analyzed weekly with a multiplex panel for cytokines, chemokines and growth factors. Secretory Immunoglobulin A concentration will also be assayed. Exact recordings of each feeding, in terms of volume, volume of human milk, and volume of formula and fortifiers will be done. In addition, weekly stool samples will be collected from diapers for a weekly analysis of fecal calprotectin, known to be an early marker of enteral pathophysiology. Skin immunity will be assessed as a potential biomarker of immunocompetency through the use of a small tape applied to the forehead, then removed and assayed for a panel of skin immune components and cytokines by multiplex assay. Other clinical outcomes will include time to oral feeding, weight gain, time to discharge, and any significant adverse health outcomes such as infections or necrotizing enterocolitis. This will be the first careful study that will provide a computation of human milk factors and volumes across a NICU stay and a measurement of relationships to infant health, biomarkers and clinical outcomes. It will provide effect sizes for important relationships about which we currently know so little. PUBLIC HEALTH RELEVANCE: This project will study the relationships between human milk immunity and milk volume with clinical outcomes and immune and enteral biomarkers in preterm infants while hospitalized in the neonatal intensive care unit.